The high-resolution infrared spectrum of ethylene in the 1800–2350 cm⁻¹ spectral region

Abstract

Fourier transform spectra of ethylene (C₂H₄) have been recorded in the 1800–2350 cm⁻¹ (4.3–5.6 µm) spectral region using a Bruker IFS125HR spectrometer at a resolution of 0.004 cm⁻¹ leading to the observation of six vibrational bands, ν ₇ + ν ₈, ν ₄ + ν ₈, ν ₆ + ν ₁₀, ν ₆ + ν ₇, ν ₄ + ν ₆ and ν ₃ + ν ₁₀. The corresponding upper state ro-vibrational levels were fit using a Hamiltonian matrix accounting for numerous interactions. A satisfactory fit could be obtained using a polyad of nine interacting states {8¹10¹, 7¹8¹, 4¹8¹, 8¹12¹, 6¹10¹, 6¹7¹, 4¹6¹, 3¹10¹, 3¹7¹} of which three (8¹10¹, 8¹12¹ and 3¹7¹) are unobserved dark states. As a result a much more accurate and extended set of Hamiltonian constants were obtained than previously derived. The following band centers were determined: ν ₀(ν ₇ + ν ₈) = 1888.9783(20) cm⁻¹, ν ₀(ν ₄ + ν ₈) = 1958.2850(20) cm⁻¹, ν ₀(ν ₆ + ν ₁₀) = 2047.7589(20) cm⁻¹, ν ₀(ν ₆ + ν ₇) = 2178.011(60) cm⁻¹, ν ₀(ν ₄ + ν ₆) = 2252.8026(24) cm⁻¹ and ν ₀(ν ₃ + ν ₁₀) = 2171.2397(20) cm⁻¹. Finally, a synthetic spectrum that could be useful for ethylene detection in planetary atmospheres was generated.

Keywords:

• infrared
• ethylene
• rovibrational interactions
• line positions and intensities

Acknowledgements

The portion of this work that was carried out at the Optical Technology Division of NIST was supported by the Upper Atmospheric Research Program of NASA. One of the authors (JMF) thanks the Optical Technology Division for support during a stay at NIST.

Notes

Notes

1. Certain commercial equipment instruments or materials are identified in this paper to adequately specify the experimental procedure. Such identification does not imply recommendation or endorsement by the National Institute of Standards and Technology nor does it imply that the materials or equipment identified are necessarily the best available for the purpose.

2. The list of line positions and intensities is available upon request to J.−M. Flaud or W.J. Lafferty.